Fuse structures



Oct. 31, 1961 F. J. KOZACKA 3,007,020

FUSE STRUCTURES Filed Jan. 25, 1960 I IIIIIIII) gyzz zz INVENTOR.

Fred erick J Kozock'a United States Patent 3,007,020 FUSE STRUCTURES Frederick J. Kozacka, South Hampton, N.H., assignor to The Chase-Shawmut Company, Newburyport, Mass. Filed Jan. 25, 1960, 'Ser. No. 4,417 3 Claims. (Cl. 200- 132) This invention relates to fuse structures and this application is a continuation-in-part of my co-pen'ding patent application Ser. No. 806,564 for Fuse Structures, filed April 13, 1959, now US. Patent 2,939,935, issued June 7, 1960.

It is a general object of this invention to improve electric fuses of the blade contact type, as distinguished from fuses of the ferrule contact type.

It is a special object of this invention to provide a simple means for maintaining the blade contacts of electric fuses in position, and which means compensate auto matically for dimensional changes resulting from changes in ambient temperature and therefore are not adversely affected by changes in ambient temperature.

Another special object of the invention is to provide improved electric fuses comprising pin-mounted blade contacts.

Still another special object of the invention is to pro vide improved electric fuses of the type disclosed in my above-referred-to US. Patent 2,939,935.

Fuses of the type disclosed in my above referred-to US. Patent 2,939,935 include as supports for a pair of blade contacts a pair of pin-shaped springs formed of wound sheet material adapted to be radially elastically compressed and to be radially elastically expanded at spaced points thereof. According to my US. Patent 2,939,935 each of the blade-contact-supporting springs is constituted by a resilient sheet material bent substantially in the shape of a cylindrical surface, yet forming a gap which is bounded by a pair of spaced generatrices of said cylindrical surface. It is substantially the presence of this gap which imparts resilience to the pin-shaped structure. The presence of this gap imposes, however, some significant limitations upon the structure of U.S. Patent 2,939,935. One of these limitations consists in the fact that during the process of assembly some of the pulverulent filler contained in the casing enters the pinshaped springs through the lateral gaps thereof and is discharged'from the pin-shaped springs through the open axially outer ends thereof. This continuous and/or repetitive spilling or loss of pulverulent filler is rather undesirable. The aforementioned gap has also some disadvantages when the fuse according to U.S. Patent 2,939,935 performs its circuit interupting duty. The hot products of arcing then generated inside of the casing enter the pin-shaped springs through the lateral gaps thereof and then leak out through a fine gap formed between the outer surface of the casing and the inner surface of the caps or ferrules which are mounted on the casing. These fine gaps, or hair gaps, may be greatly expanded under the action of high pressures inside the casing of the fuse and this may result in a rather voluminous and highly undesirable escape of products of arcmg.

It is, therefore, another object of this invention to provide electric fuses having blade contacts mounted on and supported by pin-shaped springs and having all the advantages of such mounting of blade contacts without being subject to the aforementioned drawbacks and limitations.

These and other objects of the invention and advantages thereof will become more apparent from the following description of a preferred embodiment of the invention when taken in connection with the accompanying drawings, wherein:

3,007,020 Patented Oct. 31, 1961 FIG. l is a longitudinal section on a relatively large scale of an electric fuse embodying the invention taken along '11 of FIG. 2, the middle portion of the fuse being broken away;

FIG. 2 is a section along 22 of FIG. 1 and shows one portion of the fuse completely assembled and another portion of the fuse in the process of assembly, the middle portion of the fuse being broken away as in FIG. 1;

FIG. 3 is a cross-section through the center region of the blade-contact-carrying spring in compressed state taken along 33 of FIG. 2; and FIG. 4 is an end view seen in the direction of arrow R of FIG. 2 of the axially outer region of the bladecontac'tcarrying spring in an expanded state upon removal of the cap normally covering said region.

Referring now to the drawings, and more particularly FIGS. 1 and 2 thereof, numeral 1 has been applied to indicate a tubular casing of insulating material, e.g. a synthetic-resin-glass-cloth laminate. Casing 1 is provided with a pair of diametrically arranged transverse perforations 1a on each end thereof. A pair of caps 8 is mounted on the ends of casing 1 and each cap 8 covers a pair of perforations 1a in casing 1. A pair of blade contacts 2 is arranged in a direction longitudinally of casing 1 and each blade contact 2 projects from the outside of casing 1 through a cap 8 into the inside of casing :1. To this end each cap 8 is provided with a rectangular opening 9 having the same geometric configuration as the cross-section of blade contacts 2. Each casing 1 contains a pulverulent arc-quenching filler 13 as, for instance, quartz sand, gypsum, or chalk. Washers or discs 14 of a suitable fibrous material, e.:g. asbestos, interposed between the ends of easing 1 and caps 8 preclude the loss of filler 13 through openings 9 in caps 8. Each blade contact 2 defines a transverse perforation 5 having a predetermined diameter and being arranged in alignment with a pair of perforations 1a in casing 1. Ribbon fuse link means 3 preferably made of copper, or silver, interconnect conductively the axially inner ends of blade contacts 2. To this end the axially outer ends of link means 3 are spot-brazed at 4 to the axially inner ends of blade contacts 2. The pulverulent filler 13 forms a relatively tight packing for fuse link means 3. The fuse further comprises a pair of bladecontact-supporting pin-shaped springs 6 each formed by a substantially spirally wound length of resilient sheet metal. Each spring 6, when uncompressed, has a diameter exceeding the diameter of perforations 5 in blade contacts 2, and each spring 6 is inserted into a pair of perforations 1a in casing 1 and threaded through a perforation 5 in one of blade contacts 2, and thereby compressed in the center region thereof. The axially outer ends of pin-shaped springs 6 are expanded by appropriate wedge mean-s driven into these ends. As shown on the left side of FIG. 2 such wedge means may be formed by indentations 10 in caps 8 driven into springs 6 to expand their ends beyond the outer diameter of springs 6 when unexpanded.

Pin-shaped springs 6 have a given diameter when substantially unstressed. Springs 6 must be capable of being drastically compressed in the center region and of being drastically expanded in the region of the axially outer ends thereof. These exacting requirements can well be met by forming springs 6 by substantially spirally wound lengths of resilient sheet metal, as mentioned above.

FIGS. 3 and 4 are relatively diagrammatic and drawn on a much larger scale than FIGS. 1 and 2.

It will be apparent from the foregoing that the present design precludes the escape of pulverulent filler during the manufacturing process and precludes the escape of products of arcing when the fuses blow in response to an excess current.

Instead of expanding the axially outer ends of springs 6 by indentations of caps 8, drive screws might be used for the same purpose, as more fully shown in my above referred to U.S. Patent 2,939,935. The embodiment of the invention decribed and illustrated above, however, is preferable since it dispenses with such additional parts as drive screws and precludes escape of pulverulent filler as Well as that of hot products of arcing.

While I have described what is at present considered the preferred embodiment of the invention, it will be understood that various modifications and changes may be made without departing from the spirit and scope of the invention as defined in the following claims.

I claim as my invention:

1. An electric fuse comprising a tubular casing of insulating material having a pair of diametrically arranged transverse perforations on each end thereof; a pair of blade contacts arranged in a direction longitudinally of said casing and projecting from the outside of said casing to the inside thereof, each of said pair of blade contacts having a transverse perforation of predetermined diameter and being arranged in alignment with a pair of said perforations in said casing; ribbon fuse link means conductively interconnecting the axially inner ends of said pair of blade contacts; a pulverulent arc-quenching filler inside said casing closely surrounding said fuse link means; a pair of pin-shaped springs formed by substantially spirally wound lengths of resilient sheet metal, each of said pair of springs having when uncompressed a diameter exceeding the diameter of said perforation in each of said pair of blade contacts, each of said pair of springs being inserted into a pair of said perforations in said casing and threaded through said perforation in one of said pair of blade contacts and thereby compressed in the center region thereof; and wedge means driven into the outer ends of each of said pair of springs and expanding said ends beyond the outer diameter of each of said pair of springs when unexpanded.

2. An electric fuse comprising a tubular casing of insulating material having a pair of diametrically arranged transverse perforations on each end thereof; a pair of caps each mounted on one of the ends of said casing and each covering a pair of said perforations in said casing; a pair of blade contacts arranged in a direction longitudinally of said casing each projecting from the outside of said casing through one of said pair of caps into the inside of said casing, each of said pair of blade contacts having a transverse perforation of predetermined diameter and being arranged in alignment with a pair of said perforations in said casing; ribbon fuse link means conductively interconnecting the axially inner ends of said pair of blade contacts; a pulverulent arc-quenching filler inside said casing closely surrounding said fuse link means; a pair of pin-shaped springs formed by substantially spirally wound lengths of resilient sheet metal, each of said pair of springs having when uncompressed a diameter exceeding the diameter of said perforation in each of said pair of blade contacts, each of said pair of springs being inserted into a pair of said perforations in said casing and threaded through said perforation in one of said pair of blade contacts and thereby compressed in the center region thereof; and wedge means formed by indentations in said pair of caps driven into the outer ends of said paii, of springs and expanding said ends beyond the diameter of said pair of springs when unexpanded.

3. An electric fuse comprising a tubular casing of insulating material having a pair of diametrically arranged transverse perforations on each end thereof; a pair of blade contacts arranged in a direction longitudinally of said casing and projecting from the outside of said casing to the inside thereof, each of said pair of blade contacts having a transverse perforation of predetermined diameter and being arranged in alignment with a pair of said perforations in said casing; ribbon fuse link means conductively interconnecting the axially inner ends of said pair of blade contacts; a pulverulent arcquenching filler inside said casing surrounding said fuse link means; a pair of pin-shaped springs formed by windings of sheet metal each defining a tubular duct open only at the ends thereof, each of said pair of springs having when uncompressed a diameter exceeding the diameter of said perforation in each of said pair of blade contacts, each of said pair of springs being inserted into a pair of said perforations in said casing and threaded through said perforation in one of said pair of blade contacts and thereby compressed in the center region thereof; a pair of caps mounted on the axially outer ends of said casing and overlapping the axially outer ends of said pair of springs, and means for precluding relative movement between said pair of caps and said casing and said pair of springs.

References Cited in the file of this patent UNITED STATES PATENTS 1,107,861 Stout Aug. 18, 1914 1,237,211 Leveen Aug. 14, 1917 2,864,916 Barrett Dec. 16, 1958 

